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Sri Lanka; Quality of Collected Rainwater in Relation to Household Water Security

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Ariyananda Quality of Collected Rainwater in Relation to Household Water Security session 3 Quality of Collected Rainwater in Relation to Household Water Security Tanuja Ariyananda, Lanka Rain Water Harvesting Forum No.247, Wijekumaranatunge Mawatha, Kirulapone, Colombo 5, Sri Lanka E mail: tanuja@sri.lanka.netIntroductionRainwater harvesting has gained popularity in rural areas of Sri Lanka during the lastfew years through number of water supply projects funded by government as well asNGO’s. The greater attraction of the rainwater harvesting system is the low cost,simple design and construction technology, independence of central system,accessible and easily maintained at household.However, whether the systems provides the households with adequate safe water isstill a unanswered question. As water security is been defined as ‘accessibility,reliability and timely availability of adequate safe water to satisfy basic human need’(Ariyabandu). The question is how safe is rain water?. Safety of water is measured athousehold level by peoples perception and laboratory by absolute measurements. Athousehold the level of acceptability is based on cultural and socio-economic standardsand the quality of alternative water supply. In rural Sri Lankan families, taste plays amajor role in drinking water. Drinking people still prefer to use known groundwater tounknown rainwater. Reluctance to drink rainwater collected from the rooftop thoughtto be a perception of water quality. Quality of rainwater collected depends on when itis collected (after the first rain), how it is stored as well as method of use.Rainwater usersSince 1995 Community Water Supply and Sanitation project implement by Ministryof National Housing and Urban Development with World Bank assistance build morethan 6000 rain water harvesting systems in Badulla and Matara district (Ariyananda).Since then the technology developed under this project has been introduced to otherdistricts (dry zone) by various other government organisations as well as NGO’s.Today estimated 6500 systems are in operation through out the country. The twotechnology options available are: an underground brick tank modeled after theChinese biogas digester and a free standing ferrocement tanks of 5 m3 capacity.While the concept and technology has become popular there s still reluctance for thepeople to use rain water as a drinking source. Studies has reveled (Ariyabandu) thatonly 10% of these householder use the collected rainwater for drinking purposes.However other householders use it for every other purposes including cooking.Peoples perception of RainwaterTaste plays a major role in drinking water. As rainwater do not contain any mineralsand does not carry any taste it is not well accepted widely in rural Sri Lanka as meansof drinking water. However, in some part of the country where the ground water isDomestic Roofwater Harvesting Workshop 1 IIT Delhi, April 2001

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Ariyananda Quality of Collected Rainwater in Relation to Household Water Security session 3mineralized or saline rainwater is used for drinking. These households collect waterdirectly from the sky or use collected rainwater for drinking just after the rain. This isbecause debris and organic matter from badly managed roof get collected in the tankand creates a bad smell in the collected rain water due to anaerobic action or opentank breed mosquitoes after few days making the water unacceptable for drinking.Consumption of rainwater is related to perception of quality. Most of the rain watertanks are generally not tested for water quality, therefore householders has noknowledge of true water quality only perception of water quality. General quality ofrain water is measured at household level by1. presence of leaves and other material2. presence of mosquito larvae and other insects, rodents and frogs.3. color4. tasteAbsolute quality of Rain waterStudies reveled rainwater collected and stored with adequate care meets themicrobiological standard set by the WHO for drinking water ( Heijnen, & Mansur,1998). A survey conducted in five rain water collection locations reveal that, ingeneral quality of rain water collected depends on the storage and management of thesystem.Table 1 shows results of the survey conducted. Results shows that rain water collectedmeet the WHO standard for physical chemical quality except in few new tanks(Siyabaladuwa and Puttlam) the pH is little high due to cement dissolving.Conductivity, Turbidity and Hardness in all locations meet the required WHOstandards.Table 1: Survey of quality of collected water from 5 locations ins Sri LankaLOCATION pH Conductivity Turbidity Hardness F.Coliform/ µ C/cm NTU CaCO3 100ml mg/lMATARA 8.2(6-9.8) 60 (10-160) 5 0-20 28 (0-2000)BANDARAWEL 7.8 (7.1-11.5) 70(30-170) 5 0-20 11(0-400)LAWELIMADA 8.4(10.7-7) 100 (60-160) 5 0-20 75 (1-600)SIYABALADU 10.7(6.5- 220 (110- 5 0-20 0 (0-10)WA 11.5) 770)PUTTLAM 9.3-9.8 10-360 5 20 5WHO Standard 6.5-8.5 500 5 250 0However bacteriological quality (Fecal Coliform) of rain water does not meet theWHO standard except at Siyabaladuwa where all the tanks are fitted with filters. Inother places better bacterial quality water was recorded from systems fitted withfilters than without filters (Figure 2).Domestic Roofwater Harvesting Workshop 2 IIT Delhi, April 2001

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Ariyananda Quality of Collected Rainwater in Relation to Household Water Security session 3Survey also reveled that at the start of the rainy season (November) Figure 2,F.Coliform count in the tank is high due to roof washout. This contradicts the popularconcept that rain water collected during the rainy season is better quality than thestored water. However, later during the rainy season as the roof are been washed cleanthe bacterial quality become better. Fig:2 Coliform per 100ml of rainwater recorded over 6 months from Badulla district FC/100ml/Monthly Rain fall 400 300 mm 200 100 0 Sept Oct Nov Dec Jan Feb Group B with Filters Group A No filters RainfallTable 2: Chemical quality of collected rainwater from Badulla districtLocation Zn (mg/l) Cd (mg/l) Mg (mg/l) Al (mg/l) Cr (mg/l) MnBandarwela 0.5556 0.027 0.12 0.37 0 0.0043 (1.04-0) (0.034-0.016) (0.25-0.04) (0.77-0.079) (0.014-0)Welimada 0.045 0.013 0.19 0.54 0.0078 0 (0.16-0) (0.21-0.003) (0.41-0.08) (0.99-0.3) (0.015-0)WHO 3 0.003 0.6 0.2 0.05 0.5standardZinc, Magnesium Chromium and Manganese levels in the rain water tanks are wellbelow the WHO acceptable levels. However, Cadmium and Aluminum are higherthan the WHO standards. Households where Aluminum was high contained GI roofs.A comparison of Rain water with other conventional water sourcesBacterial quality of rain water collected in tanks has always been better than theconventional shallow wells in all districts sampled. In some dry zone district (Puttlamand Tangalle) hardness and conductivity in the shallow wells is higher than therecommended WHO standard. In these district people prefer to drink rainwater thanthe well water. In the wet zone (Bandarawella and Welimada) often in theconventional water sources water is acidic. This could be due to high agriculturalactivities and use of fertilizers and other chemicals in these areas.Domestic Roofwater Harvesting Workshop 3 IIT Delhi, April 2001

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Ariyananda Quality of Collected Rainwater in Relation to Household Water Security session 3 Figure 2: Water Quality of RWHT and Wells from Matara District 2500 2000 E.coli/100 ml 1500 1000 500 0 June August Sept Nov. Dec. Jan. Feb. RWHT WellsConclusionGood quality rain water can be collected and stored if the rain water harvestingsystem is managed and operated efficiently. That is if the roof is kept clean, first flushdevice and filters are used and the tank is kept closed to prevent sunlight entering tofrom algae and mosquitoes breeding. Chemical quality of rain water is not a majorconcern in the rural areas except in Tin roof. People perception of quality of waterrainwater need to changed through education and awareness raising. A simple, lowcost water quality testing systems should be designed for the householders to monitortheir own water quality.Reference1. Ariyabandu R.de.S. (1999) Water Security through Rainwater Harvesting. Paper presented at the 25th WEDC Conference Ethiopia Africa2. Ariyananda T.N. (1999) Rainwater Harvesting for Domestic Use In Sri Lanka. 25th WEDC Conference, Addis Ababa, Ethiopia. p 369-372.3. Heijnen, H and Mansur U. (1998) Rainwater Harvesting in the Community Water Supply and Sanitation Project. Proceeding of the Symposium on Rain Water Harvesting for Water Security. Feb. 1998, OUR Engineering technology Open University, Colombo, Sri Lanka.Vol.2Domestic Roofwater Harvesting Workshop 4 IIT Delhi, April 2001